The present invention relates generally to the field of telecommunications, and more specifically, to the field of cellular carrier selection.
A cellular telephone communication system typically provides services to an area by dividing the area into many smaller geographic areas, known as cells, each of which is serviced by a transmitter-receiver station, known as a cell site. The cell sites are connected through landlines, or other communication links, to so-called mobile telephone switching offices (MTSO""s) which are, in turn, connected to the public switched telephone network (PSTN). According to current FCC rules, any given area is serviced by up to two competing providers of cellular airtime communication services (i.e., cellular carriers). The two service providers in any given geographic area, commonly referred to as xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d carriers, are assigned different groups of frequencies, or frequency sets, through which services are provided along paging, control, access, and voice channels, as would be understood by those reasonably skilled in the industry and as dictated by technical standards of appropriate regulatory agencies.
According to typical contemporary billing rate structures, distinctions are made relative to whether or not the user has subscribed to airtime services with the carrier currently being accessed. If a call is originated within an area serviced by a carrier with which the caller has a pre-existing billing arrangement such that a local telephone number has been assigned to the cellular telephone by that carrier, the call can potentially be less expensive than a call made outside such a so-called xe2x80x9chomexe2x80x9d area, during which time the cellular telephone is said to be xe2x80x9croamingxe2x80x9d with respect to that carrier. A typical cellular telephone contains memory locations known as a number assignment module (NAM) in which an installer technician stores an assigned telephone number and a system identification code (SID) which uniquely identifies a particular carrier which is primarily intended to provide airtime service for that telephone. This carrier is referred to as the xe2x80x9chomexe2x80x9d carrier. Since each carrier broadcasts its unique SID in areas serviced by that carrier, a cellular telephone, in order to determine whether it is, at any given time, located within its home service area, typically scans certain frequencies to receive SIDs broadcast by the carriers and then compares the received SIDs to SIDs stored in the NAM.
xe2x80x9cAxe2x80x9d frequencies are reserved for nonwireline carriers, while xe2x80x9cBxe2x80x9d frequencies are reserved for wireline carriers. Due at least in part to anticipated cooperation between similar types of carriers, conventional cellular telephones enable users to choose among six carrier selection methods, commonly referred to as the standard A/B system selection feature. The six options include Prefer A, Prefer B, A Only, B Only, Home Only, and SID Only. According to the Prefer A option, the cellular telephone prefers to use an xe2x80x9cAxe2x80x9d frequency before using a xe2x80x9cBxe2x80x9d frequency. The Prefer B option is similar in an opposite sense. Under the A Only mode of operation, the cellular telephone uses only xe2x80x9cAxe2x80x9d frequencies, and conversely uses only xe2x80x9cBxe2x80x9d frequencies when operating under the B Only mode. Under the Home Only mode, the cellular telephone is prohibited from roaming, and under the SID Only mode, the cellular telephone can be used only when receiving one particular SID entered into memory by the user.
Recently, xe2x80x9cAxe2x80x9d carriers and xe2x80x9cBxe2x80x9d carriers have been entering into customized roaming agreements whereby cellular telephones serviced by one of the agreeing carriers are able to operate at reduced rates in areas serviced by the other carrier. Unfortunately, the standard A/B system selection options do not provide customized carrier selection functions for any purpose, including supporting customized roaming agreements between carriers. One attempt at solving this problem is disclosed in U.S. Pat. No. 4,916,728, issued to Blair. That patent discloses a carrier selection method which, when no SID matching the home SID is received, allows normal operation only when a SID that does not exist on an exclusion list (or conversely exists on a xe2x80x9cgoodxe2x80x9d list) is received. A 911 override is also provided to allow dialing of certain emergency numbers if the only SID received is on the exclusion list. That method exhibits drawbacks by potentially denying available service when both available SIDs are on the exclusion list or when the only available SID is on the exclusion list due to dead spots in, or gaps between, service areas. It is also unclear how the new mode of carrier selection affects the standard A/B system selection feature.
In addition, one type of cellular telephone, such as that disclosed in U.S. Pat. No. 5,020,091, issued to Krolopp et al., includes multiple NAMs for subscription to multiple carriers. In this way, the cellular telephone owner can take advantage of potentially lower rates in multiple geographically diverse areas by subscribing to carriers within each service area. The telephone disclosed by the ""091 patent further discloses means for prompting a user to choose to use a particular NAM when the cellular telephone is moved into an area serviced by a carrier with which the user has been assigned a local number. Consequently, the user is required to respond to such a prompt in order to benefit from the potentially more advantageous rates each time a new carrier is locationally xe2x80x9chomexe2x80x9d to the cellular telephone.
There is, therefore, a need in the industry for a system which addresses these and other related, and unrelated, problems.
Briefly described, the present invention includes, in its most preferred embodiment, a method and an apparatus for selecting a cellular carrier frequency for accessing cellular airtime services based upon a list of preferred SIDs. A cellular telephone is programmed to accept into memory a list of preferred, rather than xe2x80x9cgoodxe2x80x9d, SIDs corresponding to carriers through which service will be preferred. When an installer technician enters a SID into the preferred list, the standard A/B system selection function is, while any SID remains in the preferred list, replaced by a substitute system selection function which includes only three carrier selection modes including the Home Only mode, the SID Only mode, and a Roam Saver mode. When the Roam Saver carrier selection mode is selected by the user, while the cellular telephone will prefer service through a carrier broadcasting a SID matching a SID on the preferred list, the cellular telephone will never deny service to emergency or non-emergency destinations if any SID, including one not on the preferred list, is received by the cellular telephone.
Status indicators are used to, among other purposes, differentiate between no service being available, service being available through a carrier broadcasting a SID matching a home SID (a home carrier), service being available through a carrier broadcasting a SID matching a SID on the preferred list (a preferred SID), and service being available through a carrier broadcasting a SID not matching a home SID or a SID on the preferred list (a non-preferred available SID). In the preferred embodiment, indicator lights are employed, while alternate embodiments include status indicators taking the form of display icons, other lights or lamps, display messages, audible tones, voice messages, etc. According to the preferred embodiment, carrier status indicators are steady or intermittent depending on whether the detected SID is a preferred SID or a non-preferred SID, thus no indicator distinction is made between detection of primary carriers (carriers of the A/B type of the first home carrier) and secondary carriers (carriers of the A/B type opposite the first home carrier). Also, in addition to multiple NAMs being included to support subscriptions to services from multiple carriers, the user is provided the option of manually selecting which NAM is used or enabling the cellular telephone, through an auto-NAM function, to automatically select and use the NAM of any home carrier detected by the cellular telephone.
It is therefore an object of the present invention to provide a method and an apparatus for selecting a cellular carrier frequency for accessing cellular airtime services based upon a list of preferred SIDs.
Another object of the present invention is to provide a method and an apparatus for providing a Roam Saver carrier selection mode in which service is never denied for either emergency or non-emergency calls when any SID is detected.
Yet another object of the present invention is to provide a method and an apparatus for, through storing at least one SID in a preferred list memory location, enabling a user to select a Roam Saver carrier selection mode in which service is never denied for either emergency or non-emergency calls when any SID is detected, wherein the Roam Saver carrier selection option becomes unavailable when all SIDs are removed from the preferred list memory locations.
Still another object of the present invention is to provide a method and an apparatus for, through storing at least one SID in a preferred list memory location, enabling a user to select among only. three carrier selection options including a Roam Saver carrier selection mode for preferably selecting carriers from a preferred list, a Home Only mode for selecting only home carriers, and SID Only mode for selecting only a user-defined carrier.
Still another object of the present invention is to provide a method and an apparatus for providing status indication to distinguish between preferred carrier access and non-preferred carrier access.
Other objects, features and advantages of the present invention will become apparent upon reading and understanding the present specification, when taken in conjunction with the accompanying drawings.